Manufacture of electron discharge tubes having a photo-conductive target



April 2, 1963 A. A. TURNBULL 3,

MANUFACTURE 0F ELECTRON DISCHARGE TUBES HAVING A PHOTO-CONDUCTIVE TARGET Filed May 12, 1959 7 Sheets-Sheet 1 fl 7: I A

21 F 1 lNVENTOR ANDREW A. TURNBULL April 2, 1963 A A TURNBULL 3,034,010

MANUFACTURE OF ELECTRQN DISCHARGE TUBES HAVING A PHOTO-CONDUCTIVE TARGET 7 Sheets-Sheet 2 Filed May 12, 1959 INVENTOR ANDREW A. TURNBULL FIG. 2

AGENT April 2, 1963 A. A. TURNBULL 3,084,010 MANUFACTURE OF ELECTRON DISCHARGE TUBES HAVING A PHOTO-CONDUCTIVE TARGET Filed May 12, 1959 7 Sheets-Sheet 3 INVENTOR ANDREW A. TURNBULL April 2, 1963 A. A. TURNBULL MANUFACTURE OF ELECTRON DISCHARGE TUBES HAVING A PHOTO-CONDUCTIVE TARGET Filed May 12, 1959 7 Sheets-Sheet 4 FIG. 4

INVENTOR ANDREW l. TURNBULL in A AGENT Aprll 2, 1963 A. A. TURNBULL 3,084,010

MANUFACTURE OF ELECTRON DISCHARGE TUBES HAVING A PHOTO-CONDUCTIVE TARGET Filed May 12, 1959 7 Sheets-Sheet 5 INVENTOR ANDREW A. TURNBULL Aprll 2, 1963 A. A. TURNBULL 3,084,010

MANUFACTURE OF ELECTRON DISCHARGE TUBES HAVING A PHOTO-CONDUCTIVE TARGET 0 Filed May 12, 1959 7 Sheets-Sheet 6 FIG 1 FIG 10 KNVENTOR ANDREW A. TURNBULL April 2, 1963 A. A. TURNBULL 3,

MANUFACTURE OF ELECTRON DISCHARGE TUBES HAVING A PHOTO-CONDUCTIVE TARGET Filed May 12, 1959 '7 Sheets-Sheet 7 INVENTOR ANDREW A. TURNBULL AGENT United States Patent 3 934,016 MANUFACTURE 0E ELEQTRQN DiSQHAEGE TUBES HAVHNG A llHflTO-QQNDUCTEVE TARGET Andrew Alfred Turnbull, London, England, assigrror to North American Philips Qornpany, inc, New York, N.Y., a corporation of Delaware Filed May 12, 1W9, Ser. No. 312,641 Claims priority, application Great Britain May 1'5, 1958 14 Claims. (Cl. 316-9) This invention relates to the manufacture of electron discharge tubes having a target constituted by a photoconductive material evaporated onto a support. An example of such a tube is the television camera tube known as the Vidicon.

The photo-conductive properties of certain target materials once deposited by evaporation are liable to suffer deleterious effects due to contamination if subsequently allowed to come into contact with air. in a known method of producing a target for a Vidicon camera tube contact between the target and air is avoided. in this method, the tube is provided initially with a side arm extending from the main envelope at right angles thereto near the end face or window of the tube which constitutes the support onto which the target material is to be deposited. At a stage when the electrode structure has been assembled, a glass base sealed to the main envelope, the air removed and argon or other inert gas at a low pressure introduced, and with the tube arranged with its end face uppermost and the side arm horizontal, a crucible containing photo-conductive material located in the side arm is moved into the main envelope to a central position some distance below the collector mesh of the electrode structure, which mesh is arranged close to the end face or face plate of the tube. The crucible, collector mesh and collector anode in the region of the crucible are then heated and the photo-conductive material, usually antimony trisulphide, is evaporated from the crucible and passes through the hot mesh to deposit on the end face of the tube. The inert gas is then pumped out and the exhaust tube sealed. Finally the crucible is withdrawn into the side arm which is then sealed oil close to the main envelope. This method while avoiding contact between the target and air has the disadvantage that it involves forming the target by evaporation of target material through the collector mesh of the electrode structure, and this makes the production of uniform layers difiicult.

It is an object of the invention to provide a method of manufacturing an electron discharge device having a photo-conductive target in which method Contact between the target and air may be avoided while overcoming the disadvantage of the known method described above.

According to the present invention there is provided a method of manufacturing an electron discharge device having a photo-conductive target and comprising an envelope terminating at one end in a wind-ow providing a support for the target and at the other end in a base member or header from which the electrode structure of the device is supported. This method includes the steps of providing an elongated tube consisting of a portion having a side arm and an end portion which is to provide the envelope of the device, which end portion is terminated by the said window; providing an electrode as sembly constituted by the electrode structure secured to the base within the tube with the base remote from the window, said assembly being movable longitudinally within the tube; and providing within the tube between the electrode assembly and the window an evaporator carrying a supply of photo-conductive material; followed by the further steps of moving the evaporator within the tube to an evaporation position; evaporating the photoconductive material from the evaporator onto the window to form the target; withdrawing the evaporator into the side arrn; moving the electrode assembly longitudinally within the tube to occupy its desired final position within the said envelope; sealing the base to the envelope, and separating the envelope from the remainder of the elongated tube.

The evaporator may conveniently be mounted in a separable manner on the electrode structure in which case movement of the evaporator within the tube can be effected by moving the electrode assembly longitudinab ly within the tube. In one embodiment of the method according to the invention in which the evaporator is carried in such a manner, the said furt.-er steps include moving the electrode assembly within the tube to a first evaporation position; evaporating the photo-conductive material from the evaporator onto the window to form the target; moving the electrode assembly longitudinally away from the window; separating the evaporator from the electrode structure; withdrawing the evaporator into the side arm; moving the electrode assembly longitudinally towards the window to occupy its final desired position within the said envelope; sealing the base to the envelope; and separating the envelope from the remainder of the elongated tube. The movement of the parts within the tube may be effected by magnet means.

The method according to the invention is applicable to cases where the photo-conductive material is evaporated in vacuo and to cases where the material is evaporated in a gas under a reduced pressure. As is known, the photo-conductive material antimony trisulphide when evaporated in an inert gas under reduced pressure gives a target layer having a higher resistivity in the dark.

When the evaporation is carried out in a gas atmosphere it will, of course, be necessary at some stage to remove the gas from within the envelope of the dis charge device. This may be done partially before the base is sealed to the envelope and a final evacuation carried out in a separate pumping operation through an exhaust tube integral with the base.

In a method according to the invention, it is possible to activate or partially activate and/or de-gas the electrode structure of t e tube before sealing takes place, or even before the formation of the target layer. The activation and/or tie-gassing of the electrode structure before the formation of the target has an advantage in that gases emitted during such processing, and which might otherwise contaminate the target, may be removed before the target is formed.

The evaporator may be a cup or crucible and when the evaporation takes place in a gas atmosphere preferably is formed with a number of openings to permit convection currents set up in the gas during the evaporation to pass through the evaporator. The evaporator (as viewed from the window) comprises openings and supporting surfaces for photo-conductive material, both of which are each uniformly or substantially uniformly distributed over a cross-sectional area of the envelope which is equal, or approximately equal, to the area of the target to be produced. The evaporator may be a wire or a narrow metal strip wound in spaced turns free from interruptions and heated by induced currents. For example, the evaporator may be wound in the form of a closed spiral. A helically wound closed spiral arranged with its apex adjacent the window for the evaporation is found to give target layers of improved uniformity in thickness. By turns free from inteiruptions is meant that the wire or strip is free from junctions or material changes in cross-section which would result in non-uniform heating of the wire or strip. The photo-conductive material is conveniently provided on the evaporator by evaporation in vacuo.

Embodiments of the invention will now be described by way of example with reference to the accompanying diagrammatic drawings in which:

FIGURES 1 to 6 show vertical sections of apparatus for carrying out one embodiment of the invention, and illustrate various stages in the manufacture of a Vidicon television camera tube,

FIGURES 7 and 8 show side-elevation and plan views of an alternative form of evaporator,

FIGURE 9 shows in vertical section part of the apparatus for evaporating photo-conductive material from the evaporator of FIGURES 8 and 9 and corresponds to the manufacturing stage of FIGURE 2,

FIGURE shows in vertical section apparatus for applying photo-conductive material to the evaporator of FIGURES 8 and 9,

FIGURE 11 shows a side view partly in section of an alternative form of detachable mounting for the evaporator shown in FIGURES 7 and 8, and

FIGURE 12 shows in vertical section a modified form of part of the apparatus shown in FIGURE 1 for carrying out a further embodiment of the invention.

Referring to FIGURE 1, there is shown an elongated glass tube 1 of which the upper part 2 is to provide the envelope of the Vidicon television camera tube. Sealed to the upper end of tube 1, via a fiat fernico ring 3 is a glass end face or window 4 on the inner surface of which is deposited a transparent conductive film. Near the lower end of tube 1, there is a liquid air trap 5, the liquid air being designated 6. The extreme lower end of tube *1 is connected via a greased cone joint 7 and a further tube 8 to a vacuum pump 9.

Extending from the tube 1 below the part 2 is a side arm 10 comprising a cylindrical part 11 and a part 12 having a greater vertical dimension. Within the cylindrical part 11 is a metal block 13, for example of iron, which is a sliding fit and from which extends a fork 14 having two prongs 15. The block 13 may be moved within part 11 of the side arm 10 toward and away from the axis of the tube 1 by means of an annular magnet 16 arranged outside the part 11 and surrounding the block 13. Horizontal movement of magnet 16 results in a corresponding movement of the block 13. Thus by means of magnet 16, the prongs of the fork 14 can be moved into the tube 1 and withdrawn again into the part 12 of the side arm 10.

Passing through the wall of tube 8 is a further glass tube 17 which has an open-ended upper portion 18 extending coaxially within the tube 1 and terminating above the liquid-air trap 5. Near the end of the tube portion 18 are a number of openings 19, of which one only is shown. The portion of tube 17 external to tube 8 communicates with a mercury manometer 20 and, via a valve 21, to an argon reservoir 22.

Within the tube 1, between the side arm 10 and the trap 5 is arranged the electrode structure for the Vidicon tube consisting of a collector anode 23 and an electron gun schematically represented at 24. Remote from the gun 24 the collector anode terminates in a collector mesh 25. The electrode structure is secured by stays 26 from a glass base or header 27 to form an electrode assembly. The base 27 having an external diameter slightly less than the inner diameter of tube 1 so that the electrode assembly may be moved longitudinally within the tube 1. If desired, the base 27 may have an upturned skirt or flange, not shown. The glass base 27 is provided with an exhaust tube 28 normally closed by a seal formed by a glass bulb 29. Passing through the glass base 27 are a number of electrode pins 36, of which only two are shown. Below the glass base 27 is a socket member 31 from which extend a number of metal connectors 32 having cup-shaped ends 33 which fit over the lower ends of pins 30. The connectors 32 also pass through the socket member 31 and terminate in spring contacts 34 which are sprung against the inner surface of tube 1. The socket 31 has a tubular extension 35 which is cemented in a recess 36 in the upper surface of a cylindrical iron block 37, which also has a recess 38 in its lower surface so that the block 37 can rest on the upper portion 18 of tube 17. The block 37 has a number of passages 39 extending through it.

The collector anode 23 of the electrode structure is maintained symmetrically within the tube 1 by centralizing springs 49 welded to the anode 23 near its upper end. Secured to the outer surface of the anode 23 and at its extremity remote from the electron gun 24 is a small diameter metal or ceramic tube or socket 41. Extending from socket 41 is a bent wire stem 42 to which is welded a central cup 4-3 of stainless steel lined with silica or platinum containing a quantity of antimony trisulphide 4.

By means of an annular magnet 45 surrounding the block 37, the electrode assembly 23-27 which is indirectly supported therefrom can he slid up and down the tube 1. With the arrangement shown the magnet 45 has a gap to allow it to be moved past the side arm 10.

Surrounding the upper part 2 of tube 1 is a cooling jacket 46 containing water 47. Reference 48 indicates a rubber seal. A stainless steel ring 49 surrounds the fernico ring 3.

Having thus provided an elongated tube 1 comprising a portion having a side arm 10 and an end portion 2 which is to provide the envelope of the device, which end portion is terminated by the said window 4, provided an electrode assembly constituted by the elect-rode structure 23 25 secured to the glass base 27 within the tube 1 with the base 27 remote from the window 4, said assembly being slidable longitudinally within the tube 1, provided within the tube 1 between the electrode assembly 23-27 and the window 4 an evaporator 43 carrying a supply of photo-conductive material 44, the evaporator 43. being supported in a separable manner from the electrode structure, and provided other ancillary equipment, we will now proceed to describe the further steps.

With the valve 21 closed the tube 1 is evacuated by means of pump 9 to a pressure of about 10* millimeters of mercury. The apertures 39 in the block 37 assist in the rapid evacuation of the tube 1. The pump is then shut off by means of a valve (not shown) and valve 21 is opened to allow argon from the reservoir 22 to enter the tube 1 through the openings 19 in the upper portion 18 of tube 17. When the manometer 20 records an argon pressure of a few millimeters of mercury the valve 21 is closed. The trap 5 prevents any grease vapour from the cone joint 7 from reaching the electrode system of the Vidicon.

The electrode assembly 2327 is then raised by means of the magnet 45 surrounding the iron block 37. to the position shown in FIGURE 2 wherein the cup 43 is about 2.5 centimeters from the window 4. An eddy-current heating coil 50 supplied by a high frequency current source 51 is then placed over the jacket 46 to surround the cup 43. Cup 43 is heated thereby and the antimony trisulphide contained in it is evaporated therefrom and deposits on the window 4 in a target layer 52. Ring 49 absorbs electrical energy in the region of the window 4 and prevents undesirable heating of disc 3. The coil 50 is withdrawn and the water jacket 46 removed. The cup 43 is then allowed to cool and the electrode assembly 23-27 lowered by means of magnet 45 to the position shown in FIGURE 3. When in this position the magnet 16 is moved to the right thereby moving the block 13 in the cylindrical part 11 of the side arm 10. The magnet position is adjusted until the prongs 15 are underneath the cup 43. The electrode assembly 23-27 is then lowered by means of magnet 4-5 to its initial position as shown in FIGURE 4 so that the block 37 rests on the end of upper portion 18 of tube 17. The cup 43 is, however, retained by the prongs and the tube 41 drops away from the wire stem 42 allowing the cup 43 and wire stem 42 to be withdrawn into the part 12 of the side arm 10. This withdrawal is effected by moving the block 13 to the left by means of the magnet 16 to the position shown in FIGURE 4.

The electrode assembly 23-27 is then raised again by means of magnet 45 to the position shown in FIGURE 5, the collector mesh 25 being about 2.5 millimeters from the target layer 52. In this position the spring contacts 34 press against platinum contacts (not shown) to which appropriate electrode voltages may be applied for the purpose of activating the cathode of the electron gun 24. The tube -1 is evacuated by means of pump 9 to a pressure of about lO millimeters of mercury and the cathode activated.

The pump 9 is maintained working during the activation of the cathode to remove any gases that may be produced. When the activation and evacuation processes are complete the upper part 2 of tube 1 is sealed to the glass base 27 while maintaining the pump 9 Working to withdraw as much as possible any gases released from the glass. The vacuum is then released and tube 1 cut some distance below the sealed base 27 to release the Vidicon envelope 2. The unwanted part of the tube 1 extending beyond the base 27 is then removed and the exhaust tube 28 sealed to a glass tube 53 leading to a pump 54 (see FIGURE 6). The tube 53 has a bulbous side piece 55 containing a metal ball '56 which is raised by a magnet (not shown) to strike sharply and break the bulb 29 thereby connecting the space within the Vidicon envelope 2 with the pump 54. Any gases which may have entered the envelope 2 during the sealing of the base 27 are then pumped out by pump 54 until the pressure is about 10 millimeters of mercury or lower. The exhaust tube 28 is then sealed off at 57 close to the base 27.

In the method described above special provision has been made for removing any gases liberated during the sealing of the base 27 of the Vidicon to the main envelope 2. It has been found, however, that in practice the amount of gas liberated can be kept very small and with the use of a very efiicient pump a planar base or flanged base without any exhaust tube may be employed.

To manufacture a further Vidicon tube with the apparatus described, another electrode assembly is set up within the envelope 1 and a fresh envelope portion sealed onto the tube 1 where the original part 2 was cut oif. Thus the basic apparatus comprising the side-arm lit and all that appears below it in FIGURE 1 together with the cup 43 can be used many times over.

The apparatus above described has the advantage that the degassing of the envelope 2 and electrode assembly 2347 can be effected before the target layer 52 is formed. In the degassing operation the evaporator 42, 43 carrying the supply of photo-conductive material 44 is first located within the side arm 10 by means of the fork 14 in the same manner as has already been described in connection with the operations performed after the formation of the target 52. The electrode assembly 2327 is then moved longitudinally from within the portion of the tube 1 having the side arm 10 to within the upper portion 2. Degassing of the electrode assembly 23-27 and the envelope is effected by sliding a cylindrical oven over the tube 2 (the cooling jacket being absent), the oven temperature being about 350 C. During degassing a vacuum within the tube 1 is maintained by the pump 9. When degassing is complete the electrode assembly 23-27 is returned to within the lower part of the tube 1 having the side arm 14 and the evaporator 42-43 is moved out of the side arm 10 and mounted in a separable manner from the end of the collector anode 23 prior to being moved within the tube d to the evaporation position as previously described.

In an alternative method of carrying out the invention, the cup from which the photo-conductive material is evaporated is replaced by a planar metal spiral 60 having a 6 coating 61 of photo-conductive material as shown in FIG- URES 7 and 8. In order that the spiral can be heated by eddy currents, the outer turn of the spiral is bent at 62 and welded to the wire 42 which acts as a support for the spiral.

Apart from the substitution of the spiral for the cup the method is carried out as described above. It has been found, however, that in the stage when the photo-conductive material is evaporated onto the window 4, as shown in FIGURE 9, the spiral 60 (now shown in section) can be arranged closer thereto than can a cup.

In a particular case in which the Vidicon envelope had an internal diameter of 23 mrns. and the efiective target area was inch by inch, the spiral 60 was constituted by 5 turns of tungsten wire having a diameter of 1 millimeter. The spiral 60 had a diameter of 22 millimeters and was wound slightly tighter at the outside.

Photo-conductive material may be applied to the spiral by evaporation in vacuo by means of the apparatus illustrated in FIGURE 10.

Referring to FIGURE 10, this figure shows a bell-jar 65 resting on a flat base 66, a sealing gasket being designated 67. The space within the jar 65 is connected by a pipe 68 to an exhaust pump 69 for evacuating the said space. Resting on the base 66 within the bell-jar 65 is a platinum crucible 70 containing a supply of pure antimony trisulphide. The crucible 70 is electrically connected to terminals 71 and 72 which pass through the base 66 and are connected by conductors 73 and 74 to a current supply source '75. Extending from the base 66 and within the bell-jar 65 is a support 76 having an arm 77 for clamping the wire 42 with the spiral 60 symmetrically above the crucible 7t and spaced therefrom at a distance of, for example, about 4.5 inches. To evaporate the antimony trisulphide, the bell-jar 65 is first exhausted to 10- millimeters of mercury by pump 69. The crucible 7 0 is then heated by current from source 75. By carrying out the evaporation in a high vacuum a very uniform layer can be produced on the spiral 60. The vacuum is then released and the coated spiral assembly detachably mounted to the end of the Vidicon electrode structure as is shown in FIGURE 9.

FIGURE #11 shows an alternative form of mounting for the evaporator of FIGURE 7, the spiral 60 being attached by means of a wire stem 80 to a circular cover 81 which can be fitted over the end of the collector anode 23 (see FIGURE 9). The socket 41 in this case can be dispensed with.

FIGURE 12 shows a modified form of part of the apparatus shown in FIGURE 1, in which the internal diameter of the part 2 of the elongated tube 1 is smaller than that of the remainder of the tube. The apparatus of FIG- URE 12 employs the evaporator mounting of FIGURE 1-1 and shows the spiral 61 supported from cover 81 which fits over the end of the collector anode 23 of the electrode assembly 23-27 in such manner that it can be readily separated from the anode 23. The electrode assembly 2327 is the same as has been described with reference to FIG- URE l and is similarly supported from the socket 31 by means of connectors 32. The socket 31 in this case does not have the tubular extension 35 as in the apparatus of FIGURE '1. The connectors 32, of which only two are shown but which correspond in number to the number of electrode pins of the Vidicon electrode assembly, pass through the socket 31 and are connected to conductors 82 which extend for some distance within the tube 1. Conductors 82 support the socket 3.1 and electrode assembly 23-27 from an iron block 83. The block 83 consists of a number of insulated segments to each of which one of the conductors 32 is electrically connected.

, Passing through the wall of tube 8 are a number of supply wires 84 which each extend through a segment of the block 83 to within the region of the side arm 1th The wires 84 are a sliding fit in block 83 so that when the block '83 is raised within the tube 1 by means of annular 7 magnet 85 electrical connection is maintained between the wires 84 and the electrode pins 30 of the electrode assembly.

The sequence of operations is the same as that described with reference to FIGURES 1 to 6. By means ofm-agnet 85 the block ,83 is raised to introduce the electrode assembly 23-27 and the evaporator spiral 60 supported therefrom into the upper part 2 of the tube ,1. Springs 40 act to maintain the assembly central within the pant 2. The electrode assembly is raised, untila suitable evaporating position is reached and the photconductive material 60 evaporated off by means of eddy current heating as described with reference to FIGURE 9. The assembly is then lowered and by. means of fork 14 attached to the block 13 in the cylindrical part 11 of side arm 10, the spiral and cover assembly is withdrawn into the side arm in a mannersimilarto that for the evaporator cup arrangement described with reference to FIGURES 3 and 4. The electrode assembly is then raised again to the final desired position within the Vidicon envelope part 2, the corresponding position 85' of the magnet 85 being shown by broken lines, the electrode structure activated and base 27 sealed to the part 2 as previously described. The necessary voltage and current supplies for the activation of the electrode structure are applied by way of the wires 84.

It will be seen that when the electrode assembly 23-27 is raised to within the tube part 2, the cover 81 will extend substantially completely over (the transverse cross-section of the end portion 2 of the tube 1. The cover 81 thus considerably reduces the likelihood of the evaporated photo-conductive material being deposited on any of the electrode parts, and in particular on the cathode of the electron gun 24, which would be deleteriously affected should such deposition occur.

Although in FIGURE 12 the cover 81 is shown fitted over the end of the collector anode 23, this is not nieces saryandth'e cover may simply consist of a flat disc which can rest on the end of the anode 23.

What is claimed is:

l. A method of manufacturing an electron device com prising an elongated envelope having at one end a photoconductive target and at the other end a base terminal member supporting an intermediate electrode structure, which comprises the steps of mounting the envelope with its base end open onto apparatus containing the electrode structure supported on the base member and adapted for movement along a given path into the envelope, moving an evaporator containing" photo-conductive material through the base end of the envelope toan evaporating position within the envelope, evaporating photo-conductive material to form the target, Withdrawing the evaporator from the envelope and outside of said given path, thereafter moving the electrode assembly on the base member through the base end of the envelope to its operating position therewithin, sealing the base member to the base end of the envelope, and separating the envelope from the apparatus. 4

2. A method as set forth in claim 1 wherein the electrode structure contains a cathode, and wherein said method further comprises actuating said cathode while the apparatus is evacuated and after the evaporation step but before the sealing step.

3. A method of manufacturing an electron device comprising an elongated envelope having at one end a photo-conductive target and at the other end a base terminal member supporting an intermediate electrode struc ture, which comprises the steps of mounting the envelope with its base end open onto apparatus containing a side tubulation communicating with its interior and also a tubular portion below the envelope and containing the electrode structure supported on the base member, removably mounting an evaporator containing photo-conductive material on a portiOH 9f the electrode structure remote s t from the base member, moving the electrode structure through the base end of the envelope until the evaporator occupies an evaporating position within the envelope, evaporating photo-conductive material onto the said one end of the envelope/to form the target, removing the electrode structure from the envelope, removing the evaporator from the electrode structure and withdrawing the evaporator into the side tubulation, moving the electrode assembly on the base member back through the base end of the envelope to its operating position within the said envelope, sealing the base member to the base end of the envelope, and separating the envelope from the apparatus.

4. A method a set forth in claim 3 further comprising degassing said electrode structure and envelope prior to mounting of the evaporator on the electrode structure.

5. A method of manufacturing an electron device comprising an elongated envelope having at one end a photoconductive target and at the other end a base terminal member supporting an intermediate electrode structure, which comprises the steps of mounting the envelope with its base end open onto apparatus containing a side tubulation communicating with its interior and also a tubular portion below the envelope and containing the electrode structure supported on the base member, locating an evaporator containing a supply of photo-conductive material within the side tubulation, moving the electrode structure into the envelope, heating the electrode structure and envelope to dega's same, withdrawing the electrode structure from within the envelo'pe,,moving .the evaporator out of the side tubulation and detachably mounting same on the electrode structure, moving the electrode structure containing the evaporator through the base end of the envelope to an evaporating position within the envelope, evaporating photo-conductive material onto the said one end of the envelope to form the target, withdrawing the electrode assembly from the envelope, detaching the evaporator from the electrode structure and withdrawing same into the side tubulation, moving the electrode assembly back into the envelope to its operating position within the said. envelope, sealing the base member to the base end of the envelope, separating the envelope from the apparatus, evacuating the envelope, and sealing oil the evacuated envelope.

6. A method of manufacturing an electron device comprising an elongated envelope having at one end a photoconductive target and at the other end a base terminal member supporting an intermediate electrode structure, which comprises the steps of mounting the envelope with its base end open onto apparatus containing a side tubulation communicating with its interior and also a tubular portion below the envelope and containing the electrode structure supported on the base member, removably mounting an evaporator containing photo-conductive material on a portion of the'electrode structure remote from the base member, magnetically moving the electrode through the base end of the envelope until the evaporator occupies an evaporating position within the envelope, evaporating photo-conductive material onto the said one end'of the envelope to form the target, magnetically removing the electrode structure from the envelope, magnetically removing the evaporator from the electrode structure and magnetically Withdrawing theevaporator into the side .tubulation, magnetically moving the electrode assembly on the base member back through the base end of the envelope to its operating position within thesaid envelopefsealing the base member to the base end of the envelope, and separating the envelope from the apparatus.

7. A methoda'ccording to claim 1 further comprising evacuating said apparatus and envelope at least prior to said evaporating step. e N

8. A method according to claim 7 further comprising introducing an inert gas at a predetermined low pressure into said apparatus and envelope between said evacuating and evaporating steps, and subsequently re-evacuating said apparatus and envelope at least after said evaporating step.

9. A method according to claim 3 further comprising evacuating said apparatus and envelope at least prior to said evaporating step.

10. A method according to claim 9 further comprising introducing an inert gas at a predetermined low pressure into said apparatus and envelope between said evacuating and evaporating steps, and subsequently re-evacuating said apparatus and envelope at least after said evaporating step.

'11. A method according to claim 5 further comprising evacuating said apparatus and envelope, said step of evacmating said apparatus and envelope occurring at least prior to said evaporating step.

12. A method according to claim 11 further comprising introducing an inert gas at a given pressure into said apparatus and envelope between said evacuating and evaporating steps, and subsequently re-evacuating said ap- 10 paratus and envelope at least after said evaporating step and prior to said sealing-off step.

13. A method according to claim 6 further comprising evacuating said apparatus and envelope at least prior to said evaporating step.

14. A method according to claim 13 further comprising introducing an inert gas at a predetermined low pressure into said apparatus and envelope between said evacmating and evaporating steps, and subsequently re-evacuatin said apparatus at least after said evaporating step.

References Cited in the file of this patent UNITED STATES PATENTS 2,600,121 McGee et a1. June 10, 1952 2,667,600 Goff Ian. 26, 1954 2,733,115 Vine Jan. 31, 1956 2,744,808 Ruedy May 8, 1956 2,809,087 Veith Oct. 8, 1957 FOREIGN PATENTS 61,104 Netherlands May 15, 1948 

1. A METHOD OF MANUFACTURING AN ELECTRON DEVICE COMPRISING AN ELONGATED ENVELOPE HAVING AT ONE END A PHOTOCONDUCTIVE TARGET AND AT THE OTHER END A BASE TERMINAL MEMBER SUPPORTING AN INTERMEDIATE ELECTRODE STRUCTURE, WHICH COMPRISES THE STEPS OF MOUNTING THE ENVELOPE WITH ITS BASE END OPEN ONTO APPARATUS CONTAINING THE ELECTRODE STRUCTURE SUPPORTED ON THE BASE MEMBER AND ADAPTED FOR MOVEMENT ALONG A GIVEN PATH INTO THE ENVELOPE, MOVING AN EVAPORATOR CONTAINING PHOTO-CONDUCTIVE MATERIAL THROUGH THE BASE END OF THE ENVELOPE TO AN EVAPORATING POSITION WITHIN THE ENVELOPE, EVAPORATING PHOTO-CONDUCTIVE MATERIAL TO FORM THE TARGET, WITHDRAWING THE EVAPORATOR FROM THE ENVELOPE AND OUTSIDE OF SAID GIVEN PATH, THEREAFTER MOVING THE ELECTRODE ASSEMBLY ON THE BASE MEMBER THROUGH THE BASE END OF THE ENVELOPE TO ITS OPERATING POSITION THEREWITHIN, SEALING THE BASE MEMBER TO THE BASE END OF THE ENVELOPE, AND SEPARATING THE ENVELOPE FROM THE APPARATUS. 